Running that covers a distance farther than the traditional marathon length of 42.195 kilometers (26.21875 miles) is called ultrarunning. The event is called an ultramarathon.

There are two general types of ultramarathon events: those that cover a specified distance, and events that take place during specified time (with the winner covering the most distance in that time). The most common distances are 50 and 100 miles, or 50 and 100 kilometers. Other distances/times include double marathons, 24-hour races, and multiday races of 1000 miles or even longer. The format of these events and the courses covered are quite variable, ranging from single or multiple loops (some as short as a 400 meter track), to point-to-point road or trail races, to cross-country rogaines. Many ultramarathons, especially trail challenges, are characterized by severe course obstacles, such as inclement weather, elevation change, or rugged terrain. Many of these races are run on dirt roads or mountain paths, though some are run on paved roads as well. Usually, there are aid stations every five to fifteen km apart, where runners can replenish food and drink supplies or take a short break.

Timed events range from 6, 12, and 24 hours to 2, 3, and 6 days (known as multi-day events). Timed events are generally run on a track or a short road course, often one mile or less.

Examples include the London to Brighton run in England which is just over 54 miles (87.085 km), the Comrades Marathon run between Pietermaritzburg and Durban in South Africa which is about 89 km (55.3 miles), and the Badwater Ultramarathon between Death Valley and Mount Whitney in the United States which is 135 miles (215 km).

See more definitions in the Definitive Guide to Running Terms.